A pathway coordinated by DELE1 relays mitochondrial stress to the cytosol.

Mitochondrial fidelity is tightly linked to overall cellular homeostasis and is compromised in ageing and various pathologies1-3. Mitochondrial malfunction needs to be relayed to the cytosol, where an integrated stress response is triggered by the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) in mammalian cells4,5. eIF2α phosphorylation is mediated by the four eIF2α kinases GCN2, HRI, PERK and PKR, which are activated by diverse types of cellular stress6. However, the machinery that communicates mitochondrial perturbation to the cytosol to trigger the integrated stress response remains unknown1,2,7. Here we combine genome engineering and haploid genetics to unbiasedly identify genes that affect the induction of C/EBP homologous protein (CHOP), a key factor in the integrated stress response. We show that the mitochondrial protease OMA1 and the poorly characterized protein DELE1, together with HRI, constitute the missing pathway that is triggered by mitochondrial stress. Mechanistically, stress-induced activation of OMA1 causes DELE1 to be cleaved into a short form that accumulates in the cytosol, where it binds to and activates HRI via its C-terminal portion. Obstruction of this pathway can be beneficial or adverse depending on the type of mitochondrial perturbation. In addition to the core pathway components, our comparative genetic screening strategy identifies a suite of additional regulators. Together, these findings could be used to inform future strategies to modulate the cellular response to mitochondrial dysfunction in the context of human disease.

Molecular pathways related to the control of proliferation and cell death in 786-O cells treated with plumbagin.

Plumbagin (PLB) is a phytochemical being used for centuries in traditional medicines. Recently, its capacity to inhibit the development of human tumors has been observed, through the induction of apoptosis, cell cycle arrest, and inhibition of angiogenesis and metastasis. Here we evaluated the mechanism of action of PLB in the kidney adenocarcinoma 786-O cell line, which are metabolizing cells important for toxicology studies. After the treatment with PLB, we observed increased apoptosis and cell cycle arrest in S and G2/M phases, starting at 5 µM. In addition, PLB was cytotoxic, genotoxic and induced loss of cell membrane integrity. Regarding gene expression, treatment with 7.5 µM PLB reduced the amount of MTOR, BCL2 and ATM transcripts, and increased CDKN1A (p21) transcripts. Phosphorylation levels of yH2AX was increased and MDM2 protein level was reduced following the treatment with PLB, demonstrating its genotoxic effect. Our results suggest that PLB acts in molecular pathways related to the control of proliferation and cell death in 786-O cells.

Potential use of CXCL12/CXCR4 and sonic hedgehog pathways as therapeutic targets in medulloblastoma.

Medulloblastoma (MB) is the most common malignant brain tumor occurring in children, and although high long-term survival rates have been reached with current therapeutic protocols, several neurological injuries are still observed among survivors. It has been shown that the development of MB is highly dependent on the microenvironment surrounding it and that the CXCL12 chemokine and its receptor, CXCR4 and the Sonic Hedgehog (SHH) pathway are crucial for cerebellar development, coordinating proliferation and migration of embryonic cells and malfunctions in these axes can lead to MB development. Indeed, the concomitant overactivation of these axes was suggested to define a new MB molecular subgroup. New molecules are being studied, aiming to inhibit either CXCR4 or the SHH pathways and have been tested in preclinical settings for the treatment of cancers. The use of these molecules could improve MB treatment and save patients from aggressive surgery, chemotherapy and radiotherapy regimens, which are responsible for severe neurological consequences. This review aims to summarize current data about the experimental inhibition of CXCR4 and SHH pathways in MB and its potential implications in treatment of this cancer.